Aperiodic disturbance suppression circuits



April 8, 1941. a. D. H. TELLEGEN 2.237.457

APERIODIC DISTURBANCE SUPPRESSIQN CIRCUITS Filed March 11, 1939 2Sheets-Sheet l 14 59.1

DE TECT 0Q FREQUENCIES 7'0 GRID 0F TUBE 6/ NV EN TOR.

I BERN/M01150. H. TELLEGEN I BY 7%.ZM

A TTORN E Y.

April 8, 1941. B. D. H. TELLEGEN KPERIODIC DISTURBANCE SUPPRESSIONCIRCUITS Filed March 11, 1939 2 Sheets-Sheet 2 AA l vvvvvn;

, IN VEN TOR.

BERNARDUS D.H.TELLE6EN A TTORNE Y.

Patented Apr. 8, 1941 UNITED STATES PATENT OFFICE APERIGDIC DISTURBANCESUPPRESSION CIRCUITS Bernardus D. H. Tellegen, Eindhoven, Netherlands,assignor, by mesne assignments, to Radio Corporation of America, NewYork, N. Y., a corporation of Delaware Application March 11, 1939,Serial No. 261,257 In the Netherlands June 24,1938

Claims.

low frequency amplifier inoperative during the 5 duration of adisturbance. Such a device may not be actuated, as a matter of course,by the desired signal, and it has, therefore, been proposed to constructthe device in such manner that it only responds to disturbanceamplitudes 10. which are larger than double the carrier wave amplitudeof the desired signal, for with a modulation depth of 100% the maximalsignal amplitude is equal to double the carrier wave ampli tude. Onlydisturbance voltages larger than douj ble the carrier wave amplitude canactuate the said device, and thus block up the low frequency amplifier.In order to be able also to suppress smaller disturbance voltages it hasbeen proposed to have the device for making the low frequency amplifierinoperative actuated by voltages set up Within a frequency spectrumwhich is not occupied by a broadcast transmitter, and which is locatedas close as possible to the received frequency spectrum. The thresholdvalue over '25 which disturbance elimination takes place may be taken inthis case as low as desired. This entails, however, the followingdrawbacks. Firstly, an unoccupied frequency spectrum can rarely befound, and, when found, it is generally not located close to the desiredsignal. Throughout the entire frequency spectrum the disturbance voltagedoes not have, in general, a constant intensity, so that in thesecircumstances the low frequency amplifier becomes inoperative when it isnot necessary, or, inversely, is not made inoperative when it isnecessary.

The invention has for its object to provide a device which permits theelimination of at least part of the interfering voltages which aresmaller than twice the carrier wave amplitude.

According to the invention, this purpose is attained by supplying thereceived high, intermediate, or low frequency oscillations to anauxiliary channel which includes a filter which does not pass at leastthe carrier wave and those sideband frequencies of the high, orintermediate, frequency oscillations which correspond to the lowestmodulation frequency, or the lowest modulation frequencies of the lowfrequency oscillations respectively, while after a determined thresholdvalue has been surpassed the voltages of the remaining frequenciesactuate a device for making the low frequency amplifier inoperative. Thefilter included in th auxiliary channel may,

for example, be a band-blocking filter. Also, if the received high, orintermediate, frequency oscillations are supplied to the auxiliarychannel, the filter included in this channel may be a low, or a high,pass filter.

The voltages of the remaining frequencies are preferably supplied to abiased rectifier, so that they are not rectified until a determinedthreshold value has been surpassed, and are supplied as a control directcurrent voltage to the said device for making the low frequencyamplifier inoperative.

According to a further embodiment of the invention, the voltages of theremaining frequencies are rectified and supplied as a control directcurrent voltage to the device for making the low frequency amplifierinoperative, in such manner that this device starts operating as soon asthe said control direct current voltage surpasses a determined thresholdValue.

It is advisable slowly to control the threshold value independence onthe intensity of the carrier wave of the received signal, and this insuch manner'that the threshold values increase with an increasingintensity of the carrier wave.

It is also possible slowly to control the said threshold values independence on the value of the voltages of the remaining signalfrequencies, and this in such manner that the threshold values increasewith an increasing value of the said voltages, in which event meansshould preferably be provided to prevent the threshold values fromexceeding a predetermined value, which maximum threshold value may bedetermined in this case by the intensity of the carrier wave of l thereceived signal.

The invention affords the possibility of suppressing part of thedisturbances which are smaller than double the carrier wave amplitude,since the device for making the low frequency amplifier inoperative cannow be actuated by disturbance voltages which are larger than the signalvoltages furnished by the high modulation frequencies which are located,for example, over 2500 cycles per second, which signal voltages areconsiderably smaller than double the carrier wave amplitude. Themodulation depth of the frequencies over 2500 cycles per second is underordinary conditions at the most about 10%. If the auxiliary channel isbranched from the high, or intermediate, frequency amplifier, th carrierWave as well as the frequency corresponding to the lowest modulationfrequency have to be suppressed in this auxiliary channel. Use may bemade for this purpose of a band-blocking filter,

but it is also possible to utilize a high, or low pass filter with theaid of which not only the carrier wave and the low modulationfrequencies, but also the remainder of one of the side-bands can besuppressed. There is thus obtained the advantage that for theelimination of aperiodic disturbances that side-band may be utilizedwhich is not disturbed by a transmitter adjacent as to frequency. If,namely, one of the side-bands of the received signal comprisesfrequencies which originate from a transmitter adjacent as to frequency,the voltages, more particularly those of the side-band frequenciescorresponding to the high modulation frequencies, have a higher value sothat the threshold below which disturbance can no longer be eliminatedalso comes to lie at a higher level.

The invention will be explained more fully with reference to theaccompanying drawings wherein,

Fig. 1 represents diagrammatically, by way of example, one embodiment ofa radio receiver having disturbance elimination according to theinvention,

Fig. 2 represents a practical example of the circuit arrangement of sucha receiver,

Fig. 3 represents a circuit arrangement for limiting the thresholdvoltage.

Referring to Fig. l, the high frequency oscillations collected by anaerial I are supplied to a high frequency amplifier 2 comprising amixing tube and, after amplification and frequency transformation, theyare passed through to an intermediate frequency amplifier 3 providedwith a detector. In the latter the intermediate frequency oscillationsare detected, and supplied to a low frequency amplifier 5 whereupon thelow frequency oscillations are made audible by a loudspeaker 6. Acontrol voltage for automatic volume control (AVG) is supplied through aconductor l to the intermediate frequency amplifier and to the highfrequency amplifier. The intermediate frequency amplifier has conectedto it a filter 1 Which does not pass the carrier wave and the sidebandfrequencies which correspond to the low modulation frequencies. Thisfilter is followed by a device 3 adapted to operate, with the aid of arelay 9, a switch iii present in the low frequency amplifier 5. Thisdevice can be actuated by voltages which pass through the filter I andis connected through a conductor I l to the intermediate frequencyamplifier 3 in order to be able to adjust the threshold value which thedisturbing voltages have to exceed in order to allow of their beingsuppressed.

Fig. 2 shows this device in detail. Similar components are denoted inFig. 2 by the same numerals as in Fig. l. The high frequencyoscillations received by an aerial i are transformed in known manner bya mixing tube 42 into intermediate frequency oscillations and supplied,through an intermediate frequency band-pass filter E3, to anintermediate frequency amplifying tube Id. In the anode circuit of thisamplifying tube is included the oscillatory circuit l5 of a secondintermediate frequency band-pass filter IT. This circuit is connected,through a condenser Hi, to a diode anode [9 arranged in a low frequencyamplifying tube 29 and, through condensers 23 and 24, to the cathode 25of this tube. By rectification there is set up across a resistance 20 acontrol direct current voltage which is supplied, through a filterformed by a resistance 2| and a condenser 22, to the control grids ofthe mixing tube I2 and of the amplifying tube [4 and which serves forthe automatic volume control.

The oscillatory circuit l6 of the intermediate frequency band-passfilter i1 is connected, on the one hand, to a diode anode 26 which isalso incorporated in the amplifying tube 29 and, on the other hand,through the parallel connection of a condenser 2'5 and a resistance 28,to the cathode of the amplifying tube 23. The low frequency voltages setup, by detection, across the resistance 28 are supplied, through a slidecontact 30 and a condenser 33, to the control grid 32 of the amplifyingtube 29. A control voltage for a cathode ray indicator which is notshown in the figure is taken from the resistance 28 through a filterformed by a resistance 33 and a condenser 34.

The amplifying tube 29 is connected, through a filter consisting of aresistance 35 and a condenser 3t and through a switch [0, to the controlgrid 31 of a final amplifying tube 38, which control grid receives,through a resistance 39, a negative bias voltage. A loudspeaker 6 isconnected, with the interposition of a transformer 4%, in the anodecircuit of the final amplifying tube 33.

The switch it is operated by a relay 9 and is constructed in such mannerthat when the current passing through the relay 9 decreases the contactis broken and the low frequency amplifier is made inoperative. Theintermediate frequency band-pass filter l3 has furthermore connected totube 4! is connected through a condenser 44 to the filter 1. This filterconsists of a parallel resonance circuit 45 which is grounded on eitherside through series resonance circuits t5 and 41. The circuits 45, 46and 47 are tuned to the intermediate frequency carrier wave.

The anode of the amplifying tube I 4 is connected, through a condenser48, to a diode anode 49 while the end of the filter l is connectedthrough a condenser 50 to a diode anode 5!. The two diode anodes 49 and5! form, together with a cathode 52, a duo-diode 53. The cathode 52 isconnected to ground through the parallel connection of a resistance 5%and a condenser 55. The anodes 49 and 5| are grounded through,resistances 56 and 57 respectively. The anode 5! is connected, through afilter consisting of a resistance 58 and a condenser 59, to the controlgrid 60 of an amplifying tube 6i in whose anode circuit is included therelay 9 in series with a resistance 62. A parallel connection of aresistance '63 and a condenser 64 provides for a bias voltage for thecontrol grid 60. The operation of this circuit arrangement is asfollows: The high frequency oscillations received by aerial I aresupplied to the control grid of mixing tube 12 in which the frequencytransformation is effected in known manner. The intermediate frequencyband-pass filter l3 connected in the anode circuit of the mixing tube 12supplies the intermediate frequency voltage received from the mixingtube l2 to an intermediate frequency amplifying tube I4 and, moreover,to an auxiliary chan- 21?]. whose input is for-medby the amplifying tubeJointly with the cathode 25, the two diode anodes l9 and 26 present inthe low frequency amplifying tube 29 provide, as has been describedbefore, in known manner, for the detection and the automatic volumecontrol. The low frequency alternating voltages set up across theresistance 35 connected in the anode circuit of the amplifying tube 25are supplied, through a separating condenser 56 and a switch which isclosed during normal reception, to the control grid 31 of the finalamplifying tube 38 by which they are amplified and then they arereproduced by the loudspeaker 6i.

The intermediate frequency oscillations supplied by the band-pass filter13, which oscillations consist of a carrier wave which, after the firstintermediate frequency selection, still has on either side a fairlylarge side-band, is supplied to the control grid d2 of the amplifyingtube 41. which is located at the input of the auxiliary channel. Theband blocking filter 'i which is included in the anode circuit of theamplifying tube 4| only passes the intermediate frequency sidebandfrequencies which correspond to the highest modulation frequencies.

Through a condenser 46 the diode 49-52 present within the duo-diode tube53 receives intermediate frequency voltage from the anode circuit of theamplifying tube 14. Since the diode Iiifor the automatic volume controlis also connected to this anode circuit this intermediate frequencyvoltage is substantially constant. The current supplied by the diode49-52 passes not only through the resistance 56 but also through theresistance 54, the latter having, jointly with the condenser 55, such atime constant that the said current only depends on the intensity of thecarrier wave of the received signal. The voltage set up by this currentacross the resistance 54 consequently constitutes for the. diode 54-52 abias Voltage which depends on the carrier wave.

To the latter diode are supplied, through a condenser 56, theintermediate frequency sideband frequencies which correspond to the highmodulation frequencies. Since the amplifying tube 41 has substantiallythe same characteristic as the amplifying tube l4, the ratio between thevoltages supplied to the two diodes 49-52 and 5I-52 remainssubstantially independent of the intensity of the desired signal, Thevalues of the resistances 54 and 56 are so chosen that the bias voltageof the diode 5l-52 exceeds the normal intermediate frequency side-bandfrequencies corresponding to the high modulation frequencies. Undernormal conditions the diode 5I-52 consequently does not rectify, so thatthe control grid 6d of the tube 6| is at ground potential.

If, however, an aperiodic disturbance whose amplitude exceeds that ofthe high modulation side-band frequencies is received by the aerial,this disturbance will surpass the threshold voltage across theresistance 54 and be rectified by the diode 5l-52 with the result thatthe diode anode 5| acquires a negative potential and imparts the latterto the control grid 60 of the tube 6|. The anode current of tube 6|which flows through the relay winding 9 consequently decreases. Thisrelay is constructed in such manner that with a decreasing current theswitch I0 is opened and the low frequency amplifier is made inoperative.If the switch [0 is located at a point in the circuit arrangement wherethere are only alternating voltages or alternating currents, the openingor closing thereof does not bring about any new disturbance.

If, consequently, there occurs an aperiodic disturbance whose amplitudeexceeds that of the side-band frequencies corresponding to the high: estmodulation frequencies, the operation of the low frequency amplifier istemporarily interrupted. If this takes place in an interval of timewhich is short enough one would not perceive anything thereof.

Fig. 3 represents a circuit arrangement wherein the threshold value overwhich disturbance elimie nation takes place, is dependent on theside-band frequencies which correspond to the high modu: lationfrequencies, and wherein this threshold value is limited by the carrierwave of the desired signal. In this case the threshold value is at anyinstant not larger than is absolutely necessary, and moreover, it cannotexceed a determined limit. In Fig. 3 elements similar to those of Fig, 2

are denoted by the same numerals, The diode anodes 49 and 5| areconnected to the band: blocking filter I through condensers 43 and 56respectively. The direct current circuit for the diode 49-52 is formedby series connected resistances 54; and 56. Across the resistance 54there is set up a direct current voltage which forms a threshold voltagefor the diode 5l-52. The value of the alternating voltage suppliedthrough the condenser 50 to this diode is ad; justed with the aid ofthis condenser in such manner that in the case of normal receptionrectification does not yet occur in the diode 5l-52. When a disturbanceis received, the latter will. be rectified and in the manner abovedescribedit causes the control grid 69 .of tube 6| to become negativewith the result that the low frequencyamplifier is made inoperative.

The circuit arrangement of Fig. 3 further come, prises a duo-diode 65.The diode anode EBthereof is connected to the cathode 52 of the firstduo-. diode 53. The other diode anode 61 is connected to ground througha coil 68, The cathode 691s grounded through the parallel connection ofa resistance 70, which is small relatively to the resistance 54, and ofa condenser H. The duodiode 65 has for its task to limit the value ofthe threshold voltage of the first duo-diode 53, for if there occurs aseries of successive disturbances, the threshold voltage across theresistance 54 gradually increases with the result that the level abovewhich the disturbances cause the low frequency amplifier to becomeinoperative, also rises. Owing to the limitation of the threshold valuethis level is also limited. If the voltage across the resistance 54exceeds a determined value which is determined by the positive voltageof the cathode 69 of the duo-diode 65 with respect to ground, the diode66-69 becomes conductive with the result that the resistance 10 inseries with the diode 66-69 is connected in parallel with the resistance54. This parallel connection causes in series with the resistance 56such a division of the direct current voltage existing across the diode49-52 that the amplitude of the disturbing voltages which give rise tothe initial rise of the threshold is larger than the partial voltageacross the parallel connection of the resistances 56 and 16, so thatthese interfering voltages are suppressed,

The positive voltage which the cathode 69 of the duo-diode 65 has withrespect to ground is determined by the value of the alternating voltageexisting between the diode anode 6'! and ground, which alternatingvoltage may inductively be taken, for example with the aid of aninductance coil 66, from the oscillatory circuit 15 which is included inthe anode circuit of the amplifying tube l4.

What is claimed is:

-1. In a side band modulated carrier receiving system of the typeprovided with a carrier demodulator and a demodulation voltageutilization. network, the improvement which comprises a network forderiving from the carrier voltage prior to demodulation voltage of sideband component frequencies corresponding to higher modulationfrequencies, means for rectifying the derived voltage, means responsiveto the carrier amplitude for controlling the operation of saidrectifying means, and means responsive to the rectified voltage forcontrolling the said utilization network.

2. In a side band modulated carrier receiving system of the typeprovided with a carrier demodulator and a demodulation voltageutilization network, the improvement which comprises a network forderiving from the carrier voltage prior todemodulation voltage of sideband component frequencies corresponding to higher modulationfrequencies, means for rectifying the derived voltage, means responsiveto said derived voltage for determining the amplitude level at whichsaid rectifying means is operative, and means responsive to therectified voltage for controlling the said utilization network.

3. In a radio receiving system having a rncdulated carrier amplifier, adetector and. audio amplifier, means for suppressing the reproduction ofdisturbances without substantially interfering with reproduction ofmodulation frequencies, said means comprising a'rnodulated carriervoltage path, said path including a filter network for passing voltagessolely of side band frequencies, corresponding to the high modulationfrequencies, a rectifier coupled to said filter network for deriving acontrol voltage from said passed voltages,

means responsive to carrier amplitude variation for controlling saidrectifier, and means responsive to the control voltage for controllingthe transmission of modulation voltage between the detector and audioamplifier.

4. A method of receiving side band modulated carrier waves Withoutinterference from disturbing electrical impulses which includescollecting modulated carrier waves and disturbance impulses,demodulating the collected waves and impulses, amplifying andreproducing the demodulated waves and impulses, deriving from thecollected waves prior to demodulation thereof voltages of side bandfrequency components corresponding to the high modulation frequencies,deriving a uni-directional control voltage from the derived voltages,controlling the amplification of said demodulated Waves in response tosaid control voltage, and simultaneously regulating the derivation ofsaid control voltage in response to collected waves.

5. A method of receiving side band modulated carrier waves withoutinterference from disturb ing electrical impulses which includescollecting modulated carrier waves and disturbance impulses,demodulating the collected waves and impulses, amplifying andreproducing the demodulated waves and impulses, deriving from thecollccted waves prior to demodulation thereof voltages of side bandfrequency components corresponding to the high modulation frequencies,deriving a uni-directional control voltage from the derived voltages,controlling the amplification of said demodulated waves in response tosaid control voltage, and simultaneously controlling the derivation ofsaid control voltage in response to the amplitude of said first namedderived voltages.

BERNARDUS D. H. TELLEGEN.

